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Nov. 18, 2010 -- E. coli O157 infection causes severe diarrhea, but that may be the least worrisome result of ingesting the toxic bug, Canadian researchers find.

Eight years after falling ill with E. coli gastroenteritis, adults have a 3.4-fold higher risk of kidney damage, a 2.1-fold higher risk of heart disease, and a 30% higher risk of high blood pressure.

The findings come from an unusual natural experiment: follow-up of a community whose water supply in May 2000 was contaminated by toxin-producing E. coli O157. In that month, heavy rainfall contaminated the poorly-chlorinated well serving Walkerton, Ontario, Canada, with fecal matter from livestock.

More than 2,300 members of the rural community fell ill with severe diarrhea. This resulted in 750 emergency room visits, 65 hospital admissions, and seven deaths.

In children (and, rarely, in adults), E. coli is known to cause a form of kidney failure called hemolytic uremic syndrome or HUS. But the long-term outcome of E. coli infection of adults hasn't been clear.

It's not a small issue. E. coli O157 outbreaks are common. In the U.S. they cause about 70,000 illnesses a year, with an average annual toll of 60 deaths and more than 2,000 hospitalizations.

E. coli O157 is among the E. coli strains that produce Shiga toxins, which can damage blood vessels -- particularly those in the kidneys. This damage is not always immediately apparent, note study authors William F. Clark, MD, professor of nephrology at Victoria Hospital, London, Ontario, Canada, and colleagues.

"Our findings underline the need for following up individual cases of food or water poisoning by E. coli O157 to prevent or reduce silent progressive vascular injury," they suggest. Annual checkups to monitor blood pressure and kidney function are advised.

The good news from the Canadian study is that only a minority of the 1,067 Walkerton adults who suffered E. coli-related illness suffered serious long-term consequences during an average eight years of follow-up.

Clark and colleagues report their findings in the Nov. 19 Online First edition of BMJ.